Many substrates are hydroscopic and permeable which means that they will absorb water from the environment. For example, under normal conditions, water accounts for about 12% to about 15% of the composition of hair. Normal hair can absorb more than 30% of its own weight in water. If the hair is damaged it has less ability to retain water within the hair fibers which gives hair its healthy appearance. It is therefore important to be able to accurately measure hair moisture to determine the overall health of hair or point of moisture in hair that offers best styling condition.
Moisture sensing devices have been developed in the past to determine the moisture level in substrates, and have relied on various techniques including resistance and capacitance measurements to obtain the desired indication. However, these methods only work well for a known cross sectional quantity and density of the substrate being measured. As the substrate density or compactness is varied, these measurement techniques fail. Additionally, these techniques rely primarily on the moisture content outside of the substrate fiber for the measurement, and do not have the ability to accurately measure moisture content within substrate fibers as well.
Other disadvantages of previous devices are that the sensor and circuit components are not coplanar. Previous devices have incorporated a coaxial cable to interconnect sensor and circuit components. This, in particular, poses difficulty in packaging the system into a hand held enclosure. In turn, it also results in increasing package costs and lower sensitivity.
Thus, there is a need for an integrated sensing device with increased sensitivity, which can accurately and reliably determine the moisture content of a substrate, such as hair, including moisture both inside and outside of the hair fiber.